The present invention relates to an improved method for melting copper base alloys containing from 2 to 12% aluminum. Essentially the method utilizes a molten flux layer to aid the melting process through the provision of melt protection. The method of the present invention results in ease of feeding additional amounts of said copper base alloy into the melt and minimization of dross formation. The molten salt cover consists essentially of a mixture of potassium and sodium chloride, with the composition of the cover being such that its melting point, fluidity, and chemical activity is consistent with the melting characteristics of the alloy in question.
It is established practice in the industry to melt copper and copper base alloys under a carbonaceous cover. The covers predominantly used in the industry consist of charcoal, graphite or lampblack either singly or in combination. These covers are essentially inert with respect to normal furnace refractories, provide protection to the molten bath from excessive oxidation during the melting procedure, and prevent excessive heat losses from the melt surface. In addition, dependent upon the choice of cover, some control may be obtained of interstitial impurities, such as carbon, oxygen and hydrogen.
The foregoing covers have attained wide spread use in the melting of a full range of copper base alloys. However, the use of these covers is associated with numerous disadvantages primarily related to the entrainment of these particulate carbonaceous covers with drosses generated during melting. The entrainment of these drosses is particularly evident in those alloys containing reducing elements, especially aluminum, which forms tenacious oxide films. Characteristically, aluminum oxides wet and entrain any particulate matter, thereby accentuating the formation of dross-cover agglomerates. The mechanical interaction of the cover with the drosses generated during melting impairs the feeding of the incoming alloy charge into the molten bath. Hence, as the melting proceeds, the process becomes increasingly inefficient realizing high melt losses and long melt down times. Moreover, metal frequently becomes entrained within the dross-cover mixtures such that the drosses removed subsequent to melting may contain very large amounts of metal which represents a significant metal loss. When preparing alloy from virgin stock, the foregoing necessitates provision of additional charge to compensate for anticipated low recoveries.
Salt covers have been proposed for a variety of alloys such as those proposed in U.S. Pat. No. 3,823,013, U.S. Pat. No. 3,754,897, East German Pat. No. 15,426 and French Pat. No. 1,197,190. These procedures are generally associated with numerous disadvantages, such as the inclusion of substantial amounts of additional components which increase the cost of the salt flux and the complexity thereof.
Accordingly, there is a need to provide an inexpensive and efficient method for melting copper base alloys utilizing an inexpensive flux material which will provide significantly improved performance characteristics. It is important to recognize that such improvements should not be obtained at the expense of either accelerated deterioration of furnace refractories, or be associated with significantly increased cost. Therefore, there is a significant commercial need for providing a relatively inexpensive method for melting aluminum containing copper base alloys which is readily useable commercially and which offers significant technical improvement and also which renders improved melting performance without attack on furnace refractories.
Accordingly, it is a principal object of the present invention to provide an improved method for melting copper base alloys containing from 2 to 12% aluminum.
It is a further object of the present invention to provide an improved method as aforesaid which is inexpensive and convenient to utilize and which renders improved melting performance without attack on furnace refractories.
Further objects and advantages of the present invention will appear hereinbelow.